The invention is based upon a method of detecting distortions of optical signals and upon a receiver for optical signals distorted due to dispersion effects as defined in the independent claims.
The publication xe2x80x9cEqualisation of Bit Distortion Induced By Polarisation Mode Dispersionxe2x80x9d by H. Bxc3xcllow, Proceedings 2 NOC 97, p. 65 to 72, has disclosed methods of treating optical signals disturbed due to polarisation mode dispersion. This publication refers to several methods of processing the disturbed signals by suitable filtering in order to recover the undisturbed, information-bearing signal. Polarisation mode dispersion occurs as an effect of the birefringence of transmission glass fibres. The signal is split into signal components corresponding to the fast and slow axes of the birefringence tensor. The two signal components here are subject to different group velocities during transmission. This leads to a delay difference xcex94t. The power in the signal components is split between the two main axes and this power distribution is defined by the parameter xcex3. Polarisation mode dispersion is a function of the temperature and the transmission conditions on the glass fibre link and changes over time. To effectively compensate for polarisation mode dispersion it would be of value to measure the two parameters xcex94xcfx84 and xcex3. Such measurement of the parameters is as yet unknown. The quoted publication also simply processes the disturbed signals in the same way by filtering, and does not firstly define the parameters of the polarisation mode dispersion. However, for a rapid, adaptive, electronic equalization of optical signals distorted by polarisation mode dispersion, it is of great advantage to predetermine the distortion by measurement technology. The object of the invention is to very rapidly detect the two parameters of the polarisation mode dispersion, even in the event of strong distortions of the signal, for example in the case of a completely closed eye in an eye diagram.
The method according to the invention comprising the characterising features of the independent claim has the advantage that the parameters of the polarisation mode dispersion are directly measured, and the result is available for analysis for an equalizer. To measure the parameters of the polarisation mode dispersion (PMD), the input signal is firstly freed of its information content resulting from the modulation of the transmitted pulses, and the thus modified, disturbed signals are analyzed.
Further advantageous embodiments and improvements of the method are described in the sub-claims.